VTOL aircraft typically fall into one of three different propulsion system categories. The first category employs a joined lift-plus-cruise propulsion system, which suffers from limited range due to inefficiencies in producing powered lift. A second category employs a tilting mechanism to turn (redirect) the force produced by the rotors from lift to cruise thrust once at a predetermined altitude. This concept, however, relies on a complex tilting mechanism that is heavy, introduces a failure path, and is costly to build and maintain.
A third category employs a series of rotors, each of which is individually dedicated to either lift or cruise thrust, where the lift rotors are only active during vertical takeoff and landing and the cruise rotor(s) are only active during the cruise portion of flight. For example, U.S. Pat. No. 8,393,564 B2 to Kroo, tilted “Personal Aircraft,” describes an aircraft configuration that uses a combination of multiple vertical lift rotors, tandem wings, and forward thrust propellers. In addition, U.S. Pat. Pub. No. 2016/0236774 to Hans Niedzballa, titled “Aircraft Capable of Vertical Takeoff,” describes an aircraft with a bearing structure having a central fuselage and two pylons each situated at a distance laterally from the fuselage. Attached to the bearing structure of the aircraft are hub rotors to provide an upward drive force acting in the vertical direction, and a thrust drive to provide thrust force acting in the horizontal direction.
Existing VTOL aircraft, such as the VTOL aircraft described by Niedzballa, suffers from a number of limitations. For example, significant vibration during transition flight is generated when a single attachment point is used between each rotor boom and the fuselage. In addition, constraining the rotor blades to the dimensions of the pylon imposes limitations on the number of rotors that may be employed in a given aircraft. Finally, in addition to added weight, cost, and complexity, stowing rotors within the rotor booms behind a closeable door does not appreciably reduce drag, can increase noise dramatically, and decreases rotor efficiency.
In view of the foregoing, a need exist for a VTOL aircraft with significant range, decreased noise, and increased efficiency.